Susan Dominus at the New York Times:
Why are babies born young? The most natural phenomenon on earth is actually hard to explain — at least on a cellular level. Consider this problem: The components of conception are old. When a woman gets pregnant, she has been carrying her egg cells since birth. The sperm that joins with the egg to form a zygote might have been just a few months in the making, but it inherits markers of age from the man who produced it. It only follows that the zygote would also show signs of age — and at first it does.
But then a mysterious metamorphosis begins: The cells of the zygote begin to reverse that damage, shaking off the metaphorical dust that the parents accumulated on their DNA. After two weeks, the cells of the embryo are back to a kind of ground zero of youth. Only then are they as young as they will ever be. To understand this process, which was discovered only recently and is known as “natural rejuvenation,” is to contemplate a mind-bending truth: We don’t start out young; we work our way back to it.
More here.
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